The overall goal of the proposed research is the development and validation of ultrasonic methods for the non-invasive, atraumatic identification and differentiation of normal, ischemic, necrotic, healing, and scarred myocardium. The hypothesis underlying this work is that physiological changes occurring in myocardium undergoing infarction alter its mechanical properties and these alterations may be reflected by changes in the acoustic properties of the tissue, specifically by changes in the frequency dependence of the ultrasonic attenuation. Making use of the receiving transducer designed to eliminate artifacts due to phase cancellation effects, we propose initially to carry out a statistically significant number of experiments in vitro on myocardial tissue obtained from dogs sacrified after periods ranging from 30 minutes through 30 days following coronary artery occlusion. Results of these ultrasonic tissue characterization studies will be correlated with an independent, quantitative index of local myocardial ischemic injury based on the depletion of creatine phosphokinase. If the hypothesis is validated in these experiments in vitro, methods are proposed for extending the technique to open-chest dogs. Validation of the efficacy and reliability of the proposed ultrasonic tissue characterization technique using animal preparations should lay the groundwork for the development of a system suitable for use in patients.